This invention relates to an improved form of dynamoelectric machine core and coil assembly that facilitates the manufacture of the assembly and any subsequent disassembly thereof that might be necessary for maintenance or repair purposes. In particular, the invention relates to an improved means for transferring heat from the coil windings of a dynamoelectric machine to the laminated core thereof, and to an improved means for limiting destructive vibration of coils in the core slots, in combination with means for preventing the formation of corona between the insulation of the coil windings and the laminated core of such a machine.
It has become fairly common practice in recent years to manufacture dynamoelectric machines, such as electric motors and generators having pre-formed coil windings, with coil winding insulation formed of epoxy resin impregnated insulating materials that are cured to form rigid, or so-called "hard sided" coils. Such epoxy resins are advantageous in that they do not soften once fully cured, so relatively close manufacturing tolerances can be used in designing and manufacturing the machines. On the other hand, it has been found that such hard sided coils tend to present the manufacturer with other problems. For example, due to the inevitable irregularities in the dimensions of the sides of the coil and the irregularities inherent in the laminated structure of the core slots in which the coils are mounted, voids exist between these parts. Such voids make it difficult to prevent the coils from vibrating in the slots when the machine is operated. Such vibration is very undesirable because it frequently causes the coil insulation to be abraded thus causing corona to be developed in high voltage machines that have a steep voltage gradient across the resultant voids. Another drawback inherent in the use of hard sided coils is that voids formed between the relatively irregular coil sides and the core slots form thermal barriers that retard the conduction of heat from the coils to the core laminations. Since the power rating of dynamoelectric machines is partially determined by the ability of the machine to dissipate heat from its coil windings, such thermal barriers are undesirable.
Prior to the present invention the foregoing disadvantages inherent in hard slot dynamoelectric machines were recognized and several solutions had been developed for them. For example, it is a known repair procedure to insert electrically semi-conductive silicone rubber into the interstices between assembled generator coil windings and the sides of core slots, in the manner disclosed and claimed in U.S. Pat. No. 3,824,683, which issued on July 23, 1974, and is assigned to the assignee of the present invention. The use of such loaded silicone rubber is effective, as is explained in that patent, to eliminate the formation of destructive corona in a hard-slot dynamoelectric machine that has been found to have voids between the coil windings and the sides of the core lamination slots, after the machine is assembled.
It is also known in the manufacture of hard-slot dynamoelectric machines to bond ridges of compressible material to the sides of winding coils prior to their insertion into laminated core slots, in order to improve the thermal conductivity between the coil sides and the laminated core. Such an assembly method and resultant dynamoelectric machine structure is disclosed and claimed in Canadian patent number 932,013 which issued on Aug. 14, 1973 and is assigned to Canadian General Electric Company, Ltd. As is pointed out in that Canadian patent, one drawback of the disclosed method and structure is that a considerable force is required to accomplish an interference fit between the coil and the coil slot into which it is inserted. In fact, several expedients are pointed out in the patent for accomplishing the desired interference fits. In that regard, it is suggested that the resin layers bonded to the coils be coated with a thin film of petroleum grease and that the slot walls be sprayed with a liquid fluorocarbon. In addition, in a supplement to the basic disclosure of that patent, it is pointed out that the resin layers bonded to the coil sides can be formed in flexible, triangular shaped ridges to facilitate the insertion of the coils into the coil slots. Beyond those admitted difficulties in utilizing the disclosed assembly, it is apparent that such interference fit might result in tearing or pulling of the resin coatings bonded to the coil sides, so that portions of the coatings might be torn away to form undesirable voids. Moreover, if it becomes necessary to disassemble the coil windings from the machine as is frequently the case for repair operations, it is obvious that such disassembly is rendered difficult due to the heavy interference fit between the bonded resin material and the sides of the coil slots.
A partial solution to the problems of assembly presented by the type of interference fit needed to practice the invention described in the above-identified Canadian patent is afforded by a prior art method of assembly wherein rectangular mats of relatively smooth sided insulating material are painted with electrically conductive paint and positioned adjacent the sides of machine core slots prior to the insertion of coils therein. Such mats tend to largely fill the inevitable clearance voids between the sides of the coils and the irregularities presented by the edges of the laminations that define the core slots. However, due to local variations in coil width, it has been found desirable in practicing this technique for reducing corona to also wedge short pieces of such electrically conductively painted mats into portions of the coil slots where voids are still found after the coil is assembled with the initial mat along its side. Such multi-layered mats have been found to be relatively effective to eliminate the formation of corona in the manufacture of high voltage dynamoelectric machines, but this multiple-layer-mat method is relatively slow and expensive to practice and does not provide as good thermal conductivity between the coils and the core structure as is often desired.
Accordingly, it is a major object of the present invention to provide an improved dynamoelectric machine core and coil assembly that is free of the problems and disadvantages of prior art methods of assembly and structures, as outlined above.
Another object of the invention is to provide an improved dynamoelectric machine core and coil assembly that is relatively easy and economical to manufacture while affording a coil mounting means that can be readily disassembled for repair.
A further object of the invention is to provide a dynamoelectric machine structure having improved electrical grounding and thermal conductivity between the insulated sides of hard coil windings and the sides of core slots in which the coils are mounted.
Still another object of the invention is to provide an improved dynamoelectric machine structure that is capable of manufacture by mass production techniques that enable conformable side fillers for winding coils to be fabricated in large sheets, rather that requiring such fillers to be bonded directly to separate coils as they are installed in a core.
Additional objects and advantages of the invention will be apparent to those skilled in the art from the description of it that follows, considered in connection with the accompanying drawings.